Range Primarily a weed of the northwestern states and southwestern Canada, but reported in every U.S. state except Alaska, Texas, Oklahoma, and Mississippi.

Discussion Sometimes classified as Centaurea stoebe ssp. micranthos. Spotted knapweed has been declared a noxious or restricted weed in at least 15 states in the U.S. and 4 Canadian province. Native to eastern Europe, it was introduced to North America in the late 1800s, probably as a contaminant in alfalfa seed or ship's ballast. It naturalized first in the San Juan Islands of Washington, and has spread rapidly across North America. It spreads aggressively and, once established, chokes out native vegetation.